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We use synchrotron radiation-induced core level photoemission spectroscopy to investigate the influence of vacancies, produced by ion bombardment, on monolayer graphene/Ni(111) exposed to CO at pressures ranging from ultra-high vacuum up to near ambient (5.6 mbar) conditions.

The ages of the oldest and most metal-poor stars in the Milky Way bear important information on the age of the Universe and its standard model. We analyze a sample of 28 extremely metal-poor field stars in the solar vicinity culled from the literature and carefully determine their ages. To this aim, we critically make use of Gaia data to derive their distances and associated uncertainties. Particular attention has been paid to the estimate of the reddening and its effect on the derivation of stellar ages. We employed different reddenings and super-impose isochrones from different sources in the stars color-magnitude diagram built up with different photometric systems. We highlight subtle metallicity effects when using the Johnson photometry for low metallicity stars and finally adopt Gaia photometry. An automatic fitting method is devised to assign ages to each individual star taking into account the uncertainties in the input parameters. The mean age of the sample turns out to be $13.9 \pm 0.5$ Gyr using Padova isochrones, and $13.7 \pm 0.4$ Gyr using BASTI isochrones. We found also a group of very metal-poor stars ($\left[\frac{Fe}{H}\right]$: -2.7 -2.0 dex) with relatively young ages, in the range 8 --10 Gyr., 23 pages, 16 eps figures, accepted for publication in the Astrophysical Journal

In this study we follow up our recent paper (Monteiro et al. 2020) and present a homogeneous sample of fundamental parameters of open clusters in our Galaxy, entirely based on Gaia DR2 data. We used published membership probability of the stars derived from Gaia DR2 data and applied our isochrone fitting code, updated as in Monteiro et al. (2020), to GB and GR Gaia DR2 data for member stars. In doing this we take into account the nominal errors in the data and derive distance, age, and extinction of each cluster. This work therefore provides parameters for 1743 open clusters and, as a byproduct, a list of likely not physical or dubious open clusters is provided as well for future investigations. Furthermore, it was possible to estimate the mean radial velocity of 831 clusters (198 of which are new and unpublished so far) using stellar radial velocities from Gaia DR2 catalog. By comparing the open cluster distances obtained from isochrone fitting with those obtained from a maximum likelihood estimate of individual member parallaxes, we found a systematic offset of $(-0.05\pm0.04)$mas., 18 pages, 23 figures

We present a detailed analysis of kinematics of the Milky Way disk in solar neighborhood using GAIA DR3 catalog. To determine the local kinematics of the stellar disks of the Milky Way galaxy we use a complete sample of 278,228 red giant branch (RGB) stars distributed in a cylinder, centered at the Sun with a 1 kpc radius and half-height of 0.5 kpc. We determine separately the kinematical properties of RGB stars for each Galactic hemisphere in search for possible asymmetries. The kinematical properties of the RGB stars reveal the existence of two kinematically distinct components: the thin disk with mean velocities ${V_R}, {V_{\phi}}, {V_Z}$ of about -1, -239, 0 km s$^{-1}$ correspondingly and velocity dispersions $\sigma_R, \sigma_{\phi}, \sigma_Z$ of 31, 20 and 11 km s$^{-1}$, and the Thick disk with mean velocities components of about +1, -225, 0 km s$^{-1}$, and velocity dispersions of 49, 35, and 22 km s$^{-1}$. We find that up to 500 pc height above/below the galactic plane, Thick disk stars comprise about half the stars of the disk. Such high amount of RGB stars with Thick disk kinematics points at the secular evolution scenario origin for the Thick disk of the Milky Way galaxy., Comment: 14 pages, 9 figures

The identification of binary stars of different mass ratios in resolved stellar populations is a challenging task. We show how the photometric diagram constructed with the pseudo-colors (H-W2)-W1 vs W2-(BP-K) can be employed to estimate the binary and multiple star ratios and the distribution of their component mass ratio $q$ effectively. As an application, we investigate the Pleiades star cluster in the range of primary component mass between 0.5 and 1.8 $M_{\odot}$. The binary star ratio is found to be between 0.54$\pm$0.11 and 0.70$\pm$0.14. On the other hand, the ratio of systems with multiplicity more than 2 is between 0.10$\pm$0.00 and 0.14$\pm$0.01. The distribution of the component mass ratio $q$ has been approximated by a power law with the exponent between -0.53$\pm$0.10 and -0.63$\pm$0.22. Below 0.5 $M_{\odot}$, we expect a large number of brown dwarfs among secondary components., 9 pages, 6 eps figure, in press in the Astronomical Journal

Due to its biocompatibility, TiO2 is a relevant material for the study of bio-interfaces. Its electronic and chemical properties are influenced by defects, which mainly consist of oxygen vacancies or adsorbed OH groups and which affect, consequently, also the interaction with biological molecules. Here we report on an x-ray photoemission spectroscopy and near edge adsorption fine structure study of glutamic acid (Glu) adsorption on the rutile TiO2(110) surface, either clean or partially hydroxylated. We show that Glu anchors to the surface through a carboxylate group and that the final adsorption state is influenced by the presence of hydroxyl groups on the surface prior to Glu deposition. Indeed, molecules adsorb both in the anionic and in the zwitterionic form, the former species being favored on the hydroxylated substrate.

Binary stars are recognized to be important in driving the dynamical evolution of stellar systems and also in determining some of their observational features. In this study, we explore the role that binary stars have in modulating the estimates of the velocity dispersion of stellar systems. To this aim, we developed a tool which allows to investigate the dependence of synthetic velocity dispersion on a number of crucial quantities characterizing the binary content: binary fraction and the distributions of their mass ratio, eccentricity and semi-major axis. As an application, we evaluate the impact that binary stars have on the estimation of the dynamical mass of dwarf spheroidal and ultra-faint dwarf galaxies, finding that it can be particularly relevant, especially for low mass and low density systems. These results bear profound implications for the interpretation of the measured velocity dispersion in such systems, since it weakens or relieves the claim for the need of large amounts of dark matter., Comment: 15 pages, 7 figures, accepted for publication in the Astrophysical Journal

In this paper we performed the deposition and self-assembly of a Pd-cyclometallated compound on Ag(1 1 0) surface for the first time. The system is investigated from the morphological and chemical point of view by scanning tunneling microscopy and x-ray photoemission spectroscopy, respectively, and the results are validated by ab-initio calculations. Our combined experimental and theoretical study aims at elucidating the atomistic details of the chemical steps following Pd cyclometallate deposition on the metallic substrate. To do that, we analyze the electronic and chemical properties of the species present on the surface at the end of the preparation process at room temperature and at 150 degrees C. We observe an unexpected complex chemistry: on one side, the organometallic molecules are found to dissociate into fragments, forming a well-ordered metal-carbon network; on the other side, Pd atoms become buried in the bulk of the metal substrate following metal exchange with surface Ag atoms. The details of this mechanistic study reveal the active role played by the metal substrate in promoting the chemistry of the deposited Pd cyclometallates and could open new perspectives for the application of this class of materials in heterogeneous catalysis.

The Pd cyclometallated complex [(5-bromo-2-phenylpyridine)Pd(μ-Cl)]2 is deposited on Ag(1 1 0) at room temperature by sublimation in ultra-high vacuum. The thermal evolution of the system is followed by scanning tunnelling microscopy and X-ray photoemission spectroscopy, while the initial and final configurations are validated by ab-initio calculations. We observe the surface induced dissociation of the molecule and the occurrence of a cross coupling reaction between the two organic fragments, leading to the surface assisted synthesis of diphenyl-bipyridine molecules. Such a process, occurring with low probability at RT, is thermally activated and competes with desorption. At variance with most cross-coupling reactions at surfaces reported in literature, in this case the reactants come from the dissociation of the same compound so that only one precursor is employed, leading to a simplified preparation protocol. The Br and Cl atoms dissociated from the molecule bind to the surface and promote an extended surface reconstruction upon annealing, which was not observed previously upon deposition of halogenated aromatic compounds.

Due to its biocompatibility, TiO

Spectroscopy from the final internal data release of the Gaia-ESO Survey (GES) has been combined with Gaia EDR3 to assign membership probabilities to targets observed towards 63 Galactic open clusters and 7 globular clusters. The membership probabilities are based chiefly on maximum likelihood modelling of the 3D kinematics of the targets, separating them into cluster and field populations. From 43211 observed targets, 13985 are identified as highly probable cluster members ($P>0.9$), with an average membership probability of 0.993. The addition of GES radial velocities successfully drives down the fraction of false positives and we achieve better levels of discrimination in most clusters over the use of astrometric data alone, especially those at larger distances. Since the membership selection is almost purely kinematic, the union of this catalogue with GES and Gaia is ideal for investigating the photometric and chemical properties of clusters as a function of stellar mass, age and Galactic position., Accepted version for publication in MNRAS. 16 pages + 38 pages of Appendices

As of 50 years ago our knowledge of the interstellar medium was summarised by Field’s theory which included two components: HI clouds and a warm and rarefied medium. This theory is based on the hypothesis of a stationary state in dynamic and thermal equilibrium, the fundamental principles of which have been set out in Sect. 4.5. In the light of the thermal stability analysis, the functional dependence of the cooling rate on the temperature is able to account for the existence of two stable phases (see Fig. 4.3).

Electrodynamics studies the behaviour of a system composed of electromagnetic fields and a conducting fluid (liquid or gaseous). The fields act on the electrons and on the ions producing currents. In turn currents cause alterations in the electro-magnetic field: hence, we have to do with a complicated coupled system of matter and fields. We focus on conductor fluids, that is, on ionised gases. The fundamental difference between a non-conducting gas and an ionised gas is related to the nature of the interaction mechanism between particles. In the case of a neutral gas the interaction forces have a very limited range; the effect on the trajectories is felt only when two particles are very close: the binary collision model well represents the situation and the kinetic theory developed starting from these ideas is able to give a correct description of the gas behaviour.

The presence of dust in the interstellar medium was highlighted by Trumpler who, in an investigation of the diameters of Galactic clusters, found a poorly convincing result: their diameters were an increasing function of distance. The origin of this result was linked to the determination of the distances made with photometry, a distance that was overestimated precisely for the absorbing action of solid dust particles. The study of the spatial distribution of these led to the conclusion that dust was associated with the interstellar gas.

The current understanding of the dynamics of gas-surface interactions is that all of the energy lost in the collision is transferred to vibrations of the target. Electronic excitations were shown to play a marginal role except for cases in which the impinging particles have energies of several electronvolts. Here we show that this picture does not hold for metal surfaces supporting acoustic surface plasmons. Such loss, dressed with a vibronic structure, is shown to make up a prominent energy transfer route down to the terahertz region for Ne atoms scattering off Cu(111) and is expected to dominate for most metals. This mechanism determines, e.g., the drag force acting on telecommunication satellites, which are typically gold-plated to reduce overheating by sunshine. The electronic excitations can be unambiguously discerned from the vibrational ones under mild hyperthermal impact conditions.

The magnetic stress tensor is defined by: $$ \sigma _{ij} = \frac{1}{\mu _0} \left( B_iB_j- \frac{B ^ 2}{2} \delta _{ij} \right) \ . $$

Blue straggler stars are exotic objects present in all stellar environments whose nature and formation channels are still partially unclear. They seem to be particularly abundant in open clusters (OCs), thus offering a unique chance to tackle these problems statistically.We aim to build up a new and homogeneous catalogue of blue straggler stars (BSS) in Galactic OCs using Gaia to provide a more solid assessment of the membership of these stars. We also aim to explore possible relationships of the straggler abundance with the parent cluster's structural and dynamical parameters. As a by-product, we also search for possible yellow straggler stars (YSS), which are believed to be stragglers in a more advanced evolution stage. We employed photometry, proper motions, and parallaxes extracted from Gaia DR2 for 408 Galactic star clusters and searched for stragglers within them after performing a careful membership analysis. The number of BBS emerging from our more stringent, selection criteria turns out to be significantly smaller than in previous versions of this catalogue. OCs are therefore not a preferable environment for these kinds of stars anymore. In addition, we found that BSS start to appear in clusters with ages larger than log(t) ~ 8.7 and are therefore absent in very young star clusters.The present catalogue supersedes the previous ones in several ways: membership assessment, number of stragglers found, and so forth. The new list includes 897 BSS and 77 YSS candidates in 408 OCs. We expect this catalogue to be the basis for a new round of studies of BSS and YSS., Comment: 9 pages, 4 figures, accepted for publication in A&A Journal on 22/02/2021

Except in particular situations, the behaviour of ordinary gases is adiabatic. In fact, due to the low values of the viscosity coefficients and thermal conductivity there is no thermal contact with the surrounding medium and the dissipation of energy by viscosity is negligible. In general, viscosity and thermal conduction are also of little importance in interstellar gas. Consider the role of thermal conduction in a molecular cloud of size \( 1\ \mathrm{pc} \), with temperature \( T = 10\ \mathrm{K} \) and density \( n = 100\ \mathrm{cm} ^{- 3} \).

Atomic diusion and mixing processes in stellar interiors influence the structure and the surface composition of stars. Some of these processes cannot yet be modelled from the first principles, and they require calibrations. This limits their applicability in stellar models used for studies of stellar populations and Galactic evolution. Aims. Our main goal is to put constraints on the stellar structure and evolution models using new refined measurements of the chemical composition in stars of a Galactic open cluster. Methods.We used medium-resolution, 19 200 R 21 500, optical spectra of stars in the open cluster NGC2420 obtained within the Gaia-ESO survey. The sample covers all evolutionary stages from the main sequence to the red giant branch. Stellar parameters were derived using a combined Bayesian analysis of spectra, 2MASS photometry, and astrometric data from Gaia DR2. The abundances of Mg, Ca, Fe, and Li were determined from non-local thermodynamic equilibrium (NLTE) synthetic spectra, which were computed using one-dimensional (1D) and averaged three-dimensional (3D) model atmospheres. We compare our results with a grid of Code d'Evolution Stellaire Adaptatif et Modulaire (CESTAM) stellar evolution models, which include atomic diusion, turbulent, and rotational mixing. Results. We find prominent evolutionary trends in the abundances of Fe, Ca, Mg, and Li with the mass of the stars in the cluster. Furthermore, Fe, Mg, and Ca show a depletion at the cluster turn-o, but the abundances gradually increase and flatten near the base of the red giant branch. The abundance trend for Li displays a signature of rotational mixing on the main sequence and abrupt depletion on the sub-giant branch, which is caused by advection of Li-poor material to the surface. The analysis of abundances combined with the CESTAM model predictions allows us to place limits on the parameter space of the models and to constrain the zone in the stellar interior, where turbulent mixing takes place., The work of E.S. was partially funded by the subsidy 3.9780.2017/8.9 allocated to Kazan Federal University for the state assignment in the sphere of scientific activities. MD acknowledges support by FCT/MCTES through national funds (PIDDAC) by these grants UIDB/04434/2020, UIDP/04434/2020 and PTDC/FIS-AST/30389/2017 and by FEDER – Fundo Europeu de Desenvolvimento Regional through COMPETE2020-Programa Operacional Competitividade e Internacionalização by this grant POCI-01-0145-FEDER-030389. MD is supported in the form of a work contract funded by national funds through Fundação para a Ciência e Tecnologia (FCT). M.D. acknowledges financial support from the “Programme National de Physique Stellaire” (PNPS) of the CNRS/INSU co-funded by the CEA and the CNES, France. We acknowledge support by the Collaborative Research centre SFB 881 (projects A5, A10), Heidelberg University, of the Deutsche Forschungsge-meinschaft (DFG, German Research Foundation). A.S. is partially supported by the grants ESP2017-82674-R (Spanish Government) and 2017-SGR-1131 (Gen-eralitat de Catalunya). TB was funded by the project grant “The New Milky Way” from the Knut and Alica Wallenberg Foundation, and project grant No. 2018-04857 from the Swedish Research Council. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www. cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/ consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell’ Istruzione, dell’ Università’ e della Ricerca (MIUR) in the form of the grant “Premiale VLT 2012”. The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. We thank Jan Rybizki for a valuable input concerning the data representation. We thank Andreas Korn for a discussion on modelling the transport of elements. We thank an anonymous referee for their comments and suggestions.

Context. NGC 2264 is a young cluster whose accretion properties can be investigated in detail by taking advantage of the FLAMES data in the context of the Gaia-ESO Survey. In fact, the analysis of the Hα emission line profile can provide us with information about the accretion and ejection activity of young stars. However, a strong nebular emission that contributes to the Hα emission can alter the profiles, with consequences for their physical interpretation. Aims. Our study is aimed at investigating the accretion and ejection properties of NGC 2264 by applying a proper treatment of the sky contribution to the Hα and forbidden emission lines (FELs; [SII] and [NII] doublets). Methods. We developed a tool, the OHαNA-method, to handle the strong nebular contribution and spectra with spurious profiles of the Hα and FELs, namely altered Hα profiles or absorption features artificially created where emission lines (FELs) are expected. We derived the quantitative measurements of relevant parameters to describe the accretion and ejection processes in young members of NGC 2264, focusing on reliable quantities derived from the width of the lines, which is relatively unaffected by the nebular emission, unlike the intensity peak, which can be altered significantly. Results. We derive the quantitative measurements related to the Hα emission line and discuss the comparison between the original and sky-subtracted spectra. We thus reveal possible profile alterations with consequences for their physical interpretation. Furthermore, we show the analysis of the variability for multi-epoch observations, also deriving the velocity of the infalling and outflowing plasma from the wings of the broad Hα emission line (in accreting stars). We also explore the mass accretion rate versus full width at zero intensity of the Hα line, namely Ṁ versus FWZI(Hα), a correlation based on the width of the emission line, which is expected to be more robust with respect to any measurement derived from the peak (e.g., Hα10%) and possibly altered by the nebular contribution. Conclusions. We are able to ascertain that more than 20% of the confirmed accretors, which have already been identified in NGC 2264, are affected by the alteration of their line profiles due to the contribution of the nebular emission. Therefore, this is an important issue to consider when investigating accretion and ejection processes in young stellar clusters. While a small fraction of spectra can be unequivocally classified as either unaffected by nebular emission or dominated by nebular emission, the majority (> 90%) represent intermediate cases whose spectral features have to be investigated in detail to derive reliable measurements of the relevant parameters and their physical implications.

Scanning tunneling microscopy (STM) and density functional theory (DFT) are used to determine the structure of mono- and bilayer iron monoxide (FeO) islands and films grown on Ru(0001). The experimental results provide information on the atomic and Moire periodicities, the height of mono- and bilayer structures, the mutual shift of crystalline lattices and their rotation with respect to the underlying single-crystal support. Based on the determined parameters, structural models of both structures are proposed. The calculations reveal the preferred stacking configurations of Fe and O layers in both structures, their stability within different high-symmetry regions of the Moire supercell (top, fcc, hcp), the interlayer spacings and the possible magnetic configurations.

We present here a novel approach to achieve the selective formation of different in-plane boron-nitrogen-carbon heterostructures on Pt(111) using a single molecular precursor, namely dimethylamine borane (DMAB). Through thermally activated decomposition and sequential bond activation it is possible to control intermolecular coupling and obtain alternatively a quasi-free-standing continuous monolayer formed by complementary hexagonal boron nitride and graphene (G) large-size domains, or a pure or doped G monolayer, or hybridized layers with non-planar bonds. The selective bond-bond coupling is achieved by controlling the substrate temperature either during or after the deposition of DMAB. This allows on-surface synthesis of B-N-C materials with tunable composition. (C) 2017 Elsevier Ltd. All rights reserved.